lecture 15 vision central pathways

Question 1

output of thalamus

Answer 1

primary visual cortex aka striate cortex, or v1, or area 17

Question 2

primary visual cortex

Answer 2

located in occipital cortex

Question 3

retinopy

Answer 3

2d surface of retina mapped onto 2d surface of thalamus and cortex

l and r visual fields seamlessly knit together despite being in very different parts of the brain

Question 4

why are the central few degrees of the visual field over-represented (magnified)

Answer 4

for better acuity in the center of the visual field

Question 4

why are the central few degrees of the visual field over-represented (magnified)

Answer 4

for better acuity in the center of the visual field

Question 5

cortical lamination

Answer 5

cortex is also layered into 1-6
but layer 4 is broken into abc and c broken into alpha and beta
after layer 6 is white matter (myelinated axons)

Question 6

neocortex

Answer 6

6-9 layers in gray matter

division of function as in lgn with different organization

much of thalamic input goes to layer 4

Question 7

cortical neurons

Answer 7

excitatory release glutamate
inhibitory release gaba

Question 8

ocular dominance columns in v1

Answer 8

Question 9

radioactive protein injected into eye

Answer 9

radioactive lgn terminals labeled by transsynaptic transport of radioactive proline containing protein injected into only one retina (white stripes)

*mainly evident in layer 4

Question 10

hubel and wiesel

Answer 10

extended kuffler’s rgc receptive field mapping first to lgn and then to v1

developed an extracellular electrode that picked up action potential activity of neurons in the vicinity of the electrode while animals looked at things

Question 11

layer 4 neurons

Answer 11

have receptive fields like rgcs
monocular
center surround

Question 12

outside layer 4

Answer 12

Question 13

receptive field properties outside IVC

Answer 13

binocular: v1 cortical neurons respond to both eyes

orientation selectivity of the receptive field in an organized pattern

Question 14

what kind of circuit could generate orientation specificity

Answer 14

parts of the pathway closer to the retina are all on or off center with antagonistic surround

maybe convergence of several center surround cells that form a line is the basis of the orientation specificity

Question 15

how would cortical neurons work together to help us see a triangle

Answer 15

Question 16

binocular stereopsis (depth perception)

Answer 16

neurons found in v1 (cat) and v2 (monkey and humans) that selectively respond to lateral disparity in r and l visual fields

Question 17

a receptive field property in upper and lower layers

Answer 17

requires binocular aligned vision

devices that simulate stereopsis by viewing two pictures (one in each eye) of the same scene from slightly different angles

based on horizontal disparity in the position of the left and right receptive fields of binocular cortical neurons

Question 18

depth perception

Answer 18

brain interprets depth by objects deviated laterally being close to you and objected deviated medially being far from you

Question 19

Visual field

Answer 19

portion of the external world that can be seen at a given time

Question 20

Ipsilateral

Answer 20

pertaining to the same side of the body

Question 21

Contralateral

Answer 21

pertaining to the opposite side of the body

Question 22

Temporal retina

Answer 22

Half of the retina closest to the temple, receives visual information from the contralateral visual field and fibers project to the ipsilateral LGN

Question 23

Nasal retina

Answer 23

Half of the retina closest
to the nose, receives visual information from the ipsilateral visual field and fibers
project to the contralateral LGN

Question 24

Optic nerve

Answer 24

bundle of retinal ganglion
axons that sends visual information from the eye to the brain before the optic chiasm. Each nerve contains axons from 1 eye, both visual field

Question 25

Optic chiasm

Answer 25

structure in the midline
where the axons from the nasal retina cross to the contralateral side

Question 26

Optic tract

Answer 26

bundle of retinal ganglion
axons after the optic chiasm. Each
nerve contains axons from both eyes, just 1 visual field, contralateral to the tract

Question 27

Lateral geniculate nucleus (LGN)

Answer 27

nucleus in the thalamus that receives visual input from
retinal ganglion cell axon and sends output to the primary visual cortex. The LGN as a whole
receives visual information from both eyes, but individual layers (6 layers in primates) including
individual neurons, receive synaptic connections from just one eye

Question 28

magnocellular

Answer 28

In primates, the most ventral layers (#1 and 2) are known as the magnocellular layers. Layer 1
receives input from the contralateral M-type RGCs and layer 2 receives input from the ipsilateral M-type RGCs

Question 29

parvocellular

Answer 29

Layers 3 through 6 are the parvocellular layers. Layers 4 and 6 receive input from the contralateral P-type RGCs and layers 3 and 5 receive input from the ipsilateral
P-type RGCs. Between the lays are numerous, tiny neurons known as koniocelluar cells that
are critical for processing color

Question 30

Optic radiation

Answer 30

axons from the LGN that carry visual information to the cortex

Question 31

Primary visual cortex (V1)/Striate cortex

Answer 31

the cortical area that receives direct input from the
LGN. The cortex is a layered structure and cells in layer 4 receive direct connections from the
LGN. Layer 4 neurons typically make synapses onto layer 2/3 neurons, which make
connections to layer 5/6 neurons and other locations in the brain. The term striate refers to the
fact that area V1 has an unusually dense stripe of myelinated axons run-in parallel to the
surface that appears white in installed sections

Question 32

Extrastriate cortex

Answer 32

areas of cortex beyond V1 that receive and respond to visual information. Receptive fields tend to change in extrastriate areas, generally retinotopy persists, but
receptive field covers a larger area of the visual field and may also respond to other visual
information (e.g. movement or shape

Question 32

Simple cell

Answer 32

descriptive term for a neuron in V1 with a receptive field shaped not like the simple center/surround
found in the retina (and LGN) but rather an elongated field
with a specific orientation

Question 33

neuronal tuning is the idea that neurons can
respond dynamically (usually firing rate) to different stimuli.
If a neuron is tuned to a particular aspect of a stimulus,
that neuron will have a greater response to the preferred
stimulus and weaker or no response to non-preferred
stimuli

Answer 33

tuning

Question 34

Orientation tuning

Answer 34

simple cells in the visual system are tuned for orientation, or edge (line)
direction

Question 35

Monocular

Answer 35

in this instance, monocular refers to neurons that are only responsive to one eye (either R or L). Neurons in the retina, LGN, and layer 4 of V1 are all monocular

Question 36

Binocular

Answer 36

in this instance, monocular refers to neurons that are only responsive stimulation of either eye. A neuron might be mored turned to either R or L, and respond weakly to stimulation of the non-tuned eye, or a neuron might respond to both eyes equally. Ocular dominance is the term used to describe the preference a neuron has for
one eye or another. Binocular neurons are found after
layer 4 in the visual system

Question 37

Columnar organization

Answer 37

Neurons within a column of
V1 (from layer 2/3 down to layer 6) have the same
tuning (e.g. same orientation selectivity), and there is an
orderly shift in orientation across a small area of V1.
Additionally, there are alternating columns of L or R
ocular dominance. Although typically drawn as a grid,
the columns are not particularly parallel or straight

Question 38

Parallel processing

Answer 38

the idea that different stimulus
attributes are process by the brain in parallel using distinct (parallel) pathways

Beyond the primary visual cortex (V1), the receptive field properties become increasingly more
complex. There are two major processing pathways out of primary visual cortex: the ventral
and dorsal streams

Question 39

Dorsal stream

Answer 39

visual processing pathway from
primary visual cortex to the parietal cortex. It is responsible for analyzing motion and depth. The
“where” stream.

Question 40

Ventral stream

Answer 40

visual processing pathway
from primary visual cortex to the temporal cortex. It is responsible for analyzing form and color. The “what” stream

Question 41

Understand visual fields. Explain how they are projected on to the retina, and how they
propagate through the LGN and then to cortex

Question 42

describe the anatomy of the visual thalamus (LGN)

Question 43

Describe the columnar organization and retinotopic (topographic) organization of visual
cortex

Question 44

Compare the receptive fields of neurons in layer IV of visual cortex to both cells in the LGN/
RGCs and the other layers in V1

Question 45

Illustrate and explain how information from both eyes combine to create binocular vision

Question 46

Cells that are inhibited by light in their center are excited by light in their surround. True or false

Answer 46

True

Question 47

Which of the following statements about center-surround receptive fields in the retina is false?

The best stimulus for an on-center cell is light in its center and darkness in its surround.

The surround portion of the receptive field is typically an annulus (or donut-shaped ring) that surrounds the circular center.

The spatial extent to which a cell can be influenced by light never extends beyond the physical extent of its dendritic field.

Answer 47

The spatial extent to which a cell can be influenced by light never extends beyond the physical extent of its dendritic field.

Question 48

Which of the following represents the most direct pathway for the transmission of visual information from the eye to the brain?

Photoreceptor->-horizontal cell–>ganglion cell–>brain

Horizontal cell–>bipolar cell–>ganglion cell–>brain

Photoreceptor–>bipolar cell–>amacrine cell–>brain

Photoreceptor–>bipolar cell–>ganglion cell–>brain

Answer 48

Photoreceptor–>bipolar cell–>ganglion cell–>brain

Question 49

In humans, at the optic chiasm _____

axons from each temporal retina decussate

axons from each nasal retina decussate

all axons leaving the eye cross over to the contralateral side

all axons from both eyes converge and then randomly segregate to each hemisphere

Answer 49

axons from each nasal retina decussate

Question 50

Ocular dominance columns in layer IV of V1 segregate input by _____.

on vs off receptive fields
different eyes
different colors
different visual hemi-fields

Answer 50

different eyes

Question 51

The parvocellular and magnocellular layers of the lateral geniculate nucleus…

receive input from the contralateral and ipsilateral halves of the visual field, respectively.

analyze the same kind of information from the visual field.

are connected to the nasal and temporal halves of the retina, respectively.

may belong to different parallel pathways.

Answer 51

may belong to different parallel pathways.

Question 52

person with damage to the ventral stream will have the most trouble with which task?

Recognizing a familiar face

Analyzing the speed of a moving target

Following the movement of a stimulus

Determining distances between objects

Answer 52

Recognizing a familiar face

Question 53

person with damage to the ventral stream will have the most trouble with which task?

Recognizing a familiar face

Analyzing the speed of a moving target

Following the movement of a stimulus

Determining distances between objects

Answer 53

Recognizing a familiar face

Question 54

Following a bicycle accident, you are disturbed to find that you cannot see anything in your left visual field. Where has the retinofugal pathway been damaged?

Answer 54

The accident has resulted in a transection of the right optic tract, resulting in blindness in the left visual field as viewed through either eye. Axons form the nasal retina of the left eye and temporal retinal of the right eye have been damaged. In contrast, a transection of the right optic nerve would render a person blind in the right eye because both nasal and temporal axons originating form the right eye would be damaged; none of the axons in the optic nerve have crossed to the opposite side of the brain. Crossing or decussation, occurs at the optic chiasm, which lies between the optic nerve and the optic tract.

Question 55

What is the source of most of the input to the left LGN?

Answer 55

receives retinal info about the right visual fields. Left LGN neurons receive synaptic input form the retinal ganglion cells in the nasal half of the right retina and the temporal half of the left retina. In the left LGN, the left eye (ipsilateral) axons synapse on cells in layers 2,3, and 5 and the right (contralateral) eye axons synapse on the cells in layers 1, 4, and 6.

Question 56

A worm has eaten part of one lateral geniculate nucleus. You cannot longer perceive motion in the right visual field off your right eye.

Answer 56

The worm has eaten magnocellular neurons in the right LGN, which corresponds to layer2. the right visual field of your right eye corresponds to the temporal retina. This info does not cross at the optic chiasm, so will project to the ipsilateral (right in this case) LGN. Motion is processed by magnocellular neurons (getting info from retinal M-cells). The magnocellular layers of LGN are the two most ventral layers, with layer 2 receiving info from the ipsilateral retina.